Passive infra-red (PIR) sensors are typically, but not exclusively, used to detect the presence of humans in a particular zone. PIR sensors find ready application in the fields of sensor lights, intruder detectors, and occupation detectors (used, for example, to switch and/or regulate lighting and/or air-conditioning systems in hotels, offices, and the like so as to conserve energy).
The Inventor is aware of conventional PIR sensors which typically include a conventional analogue PIR element connected, via a capacitive node having a high impedance, to an impedance converter for converting the high impedance to a relatively low impedance on the output of the sensor without amplification. Accordingly, an analogue signal is available at the output of the conventional PIR sensor.